The present invention relates to a control unit for an internal combustion engine, especially to a control unit for an internal combustion engine to activate quickly a three-way catalyst when the internal combustion engine starts, and to efficiently adsorb and purification HC.
The worldwide demand for energy saving and the environmental protection keeps strengthening more and more in the automotive environment in recent years, and fuel cost restriction and emission control, etc. have been reinforced.
In general, a three-way catalyst for oxidizing HC and CO in the exhaust gas exhausted to the exhaust pipe by the internal combustion engine and reducing NOx to pass emission controls has been installed in automobile engines. Although the three-way catalyst can purify HC, CO, and NOx in exhaust gas at or above a fixed temperature, it cannot usually purify enough HC, CO, and NOx at a temperature below a fixed temperature.
In general, an internal combustion engine is at low temperature when starting. Because the purification performance of exhaust gas is remarkably low for the period prior to the three-way catalyst exceeding a fixed temperature as shown in FIG. 7 (FIG. 7 shows an example of HC), it is important to activate the three-way catalyst at the early stage when starting to decrease HC, CO, and NOx in exhaust gas. Therefore, a lot of the techniques have been proposed so far.
In the technology according to the Japanese Patent Application Laid-Open No. 5-33705, by alternately supplying the rich exhaust and the lean exhaust; to the three-way catalyst, CO and HC including in the rich exhaust and O2 in the lean exhaust are made to react with each other, and the catalyst is warmed up with the heat of reaction.
Though in the aforementioned technology CO and HC in the rich exhaust and O2 in the lean exhaust are made to burn by alternately supplying the rich exhaust and the lean exhaust to the three-way catalyst, not all exhausted HC and CO necessarily burns, and the unburned components are exhausted outside through the catalyst. Therefore, HC and CO removal is not improved though the object of warming up the catalyst can be achieved. In fact, HC deterioration when starting the engine has become a big problem because of the restriction reinforcement of the exhaust gas in recent years.
The present invention arose from a consideration of these problems. An object of the present invention is to provide a control unit for an internal combustion engine in which the three-way catalyst is activated at the early stage when the internal combustion engine starts, and the deterioration of components such as HC, CO, and NOx in exhaust gas from an internal combustion engine is reduced.
A control unit for an internal combustion engine including the three-way catalyst and HC adsorbent on an exhaust side can alternately control the A/F between a rich state and a lean state in order to quicken the activation of the three-way catalyst when the internal combustion engine starts (FIG. 1).
The control unit for an internal combustion engine of the present invention configured like the above-mentioned can raise the temperature of the three-way catalyst by alternately supplying rich exhaust and lean exhaust to the three-way catalyst, and by the heat of reaction of CO, HC in the rich exhaust and O2 in the lean exhaust. In addition, by installing HC adsorbent downstream of the three-way catalyst and by supplying the rich exhaust and the lean exhaust, the three-way catalyst can be activated at the early stage without deteriorating the exhaust gas by adsorbing HC emitted downstream of the three-way catalyst by using HC adsorbent.
Moreover, a control unit for an internal combustion engine according to another embodiment of the present invention has a means for detecting completion of the evaporation of moisture in the three-way catalyst directly or indirectly. The control unit alternately controls the A/F between a rich state and a lean state in order to quicken the activation of the three-way catalyst after the completion of the evaporation of moisture in the three-way catalyst is detected (see FIG. 2). Further, the ignition time is retarded for the period until moisture in the three-way catalyst evaporates directly after the start of the internal combustion engine.
In the control unit for an internal combustion engine of the present invention configured as above-mentioned, the reason for the supply of rich/lean exhaust to the three-way catalyst is that the temperature of precious metals in the three-way catalyst are raised. If the precious metals have been partially activated, the reaction proceeds further in that part, and the activation of precious metals in the catalyst is advanced continuously by the heat of reaction. The three-way catalyst can be activated at the early stage without deteriorating the exhaust by supplying rich/lean exhaust after water in the three-way catalyst evaporates, because the heat of reaction can be efficiently supplied to precious metals if there is no moisture in the three-way catalyst. Moreover, the exhaust temperature is raised by retarding the ignition time directly after the start, whereby moisture in the catalyst evaporates promptly, and the supply of rich/lean exhaust is controlled at the early stage, because the activation time is shortened by the shortened time for water to evaporate.
Further, a control unit for an internal combustion engine according to a further embodiment of the present invention has a means for detecting the temperature of the three-way catalyst directly or indirectly. The control unit alternately controls the A/F between a rich state and a lean state in order to quicken the activation of the three-way catalyst when the temperature of the three-way catalyst is a value within the fixed range (FIG. 3).
The control unit for an internal combustion engine of the present invention configured as above-mentioned can estimate the evaporation of the moisture in the catalyst by directly or indirectly detecting the temperature of the catalyst, and control the supply rich/lean exhaust with a high degree of accuracy by setting the temperature of the catalyst to the value within the fixed range.
Further, a control unit for an internal combustion engine according to a further embodiment of the present invention has a means for detecting the operating state of the internal combustion engine. The control unit alternately controls the A/F between a rich state and a lean state in order to quicken the activation of the three-way catalyst based on the operating state (FIG. 4).
The control unit for an internal combustion engine of the present invention configured like the above-mentioned can control the supply rich/lean exhaust with a higher degree of accuracy by estimating the temperature of the catalyst and estimating the evaporation of the moisture in the catalyst based on the operating state of the internal combustion engine, for instance, the time after the engine starts, the water temperature, total air flow rate after the engine starts and so on.
Further, the control unit for an internal combustion engine according to a further embodiment of the present invention has a means for detecting the temperature of the HC adsorbent directly or indirectly. The control unit alternately controls the A/F between a rich state and a lean state in order to change the temperature of the HC adsorbent. The control unit alternately controls the A/F between a rich state and a lean state when the temperature of the HC adsorbent is within the fixed range (FIG. 5).
In the control unit for an internal combustion engine of the present invention configured as above-mentioned, the HC adsorbent has the characteristic that HC is adsorbed at a temperature below a fixed one, and is desorbed at a temperature more than a fixed one because the HC adsorbent loses the adsorbent characteristic. In general, the HC desorption temperature is much lower than the activating temperature of the three-way catalyst, i.e., the difference between these temperatures is large, and there is a temperature rise characteristic in which each phase of HC adsorbent, desorption, and purification becomes optimal. The temperature of the three-way catalyst is adjusted by controlling the supply of rich/lean exhaust appropriately paying attention to the above-mentioned. As a result, it is possible to control the temperature rise characteristic of the HC adsorbent to become optimal.
Further, a control unit for an internal combustion engine according to a further embodiment of the present invention has the three-way catalyst and HC adsorbent in the same carrier on an exhaust side alternately controls the A/F between a rich state and a lean state in order to change the temperature of the HC adsorbent (FIG. 6).
In the control unit for an internal combustion engine of the present invention configured as above-mentioned, the temperature of the three-way catalyst is raised by the heat of reaction of O2 in the lean exhaust and CO, and HC in the rich exhaust by alternately supplying the rich exhaust and the lean exhaust to the catalyst supported by the same carrier. In addition, HC separated from the three-way catalyst is adsorbed by the HC adsorbent by supplying the rich exhaust and the lean exhaust. As a result, the exhaust gas is not deteriorated, and the three-way catalyst is activated at the early stage. However, it is preferable that the temperature downstream of the catalyst is set such that the evaporation of the moisture in the three-way catalyst is not completed but the adsorbed HC in HC adsorption catalyst begins to separate.